Another problem is cuts in the Alitalia workforce of 12,800 which will be needed. It is believed that about 2,200 jobs will have to be axed.
Etihad Airways has expanded rapidly in recent years, largely on a rise of air travel in the Gulf region of the Middle East.
In a joint statement, which provided no details, the two airlines said they had agreed the "terms and conditions of a proposed transaction whereby Etihad Airways will acquire a 49% equity stake in Alitalia."
They said they would tie up the deal as soon as possible subject to approval from regulators.